Since light distribution of a halogen lamp is very similar to energy distribution of a blackbody, the halogen lamp shows excellent color rendering properties. Furthermore, color temperature of light emitted from the halogen lamp can be changed by controlling an amount of power supplied to the halogen lamp, and thus, the halogen lamp is used as a visible light source. However, there are problems that the temperature of the halogen lamp becomes extremely high since the halogen lamp emits infrared light, a reflector is required to prevent the infrared light from radiating, lifetime thereof is short compared with that of an LED, and there is much power consumption. Hence, a white light emitting device which uses light emitting diodes (LEDs) with small heat generation and longer lifetime is developed.
PTL 1 (Japanese Unexamined Patent Application Publication No. 2013-254669) discloses a color temperature variable illumination system, as a variable illuminance system capable of adjusting a color temperature and an illuminance of irradiated light in a well-balanced manner. The color temperature variable illumination system includes a light source unit having multiple types of light sources that emit light of colors different from each other, and a controller having a dial, which is rotatable, used to adjust the color temperature and the illuminance of light irradiated from the light source unit, in which the controller includes a memory which stores control curves in which the color temperature and the illuminance of light irradiated from the light source unit change in conjunction with each other; and an adjustment button used to adjust the control curves stored in the memory, and in which, when the dial is rotated, the color temperature and the illuminance of light irradiated from the light source unit change according to values determined by the control curves, respectively, which is adjusted by operating the adjustment button.